BYOND Version:490
Operating System:Windows 7 Ultimate
Web Browser:Firefox 6.0.1
Applies to:Dream Seeker
Status: Resolved (490.1103)

This issue has been resolved.
Descriptive Problem Summary: Upon movement, the players movement animation would flicker for maybe 2-3/10ths of a second, sometimes there isn't even an animation at all.

Numbered Steps to Reproduce Problem:
Set step_size to anything but it's default

Expected Results: Same animations as the previous BYOND versions

Actual Results: Choppy animations

Does the problem occur:
Every time? Or how often? Everytime
In other games? On a new project, the animations seem to work, but to an extent. They still come out slightly choppy as it would start half the animation, then go to a different part in the animation. i.e. moves left leg, moves left leg again.
In other user accounts? Not sure
On other computers? Not sure

When does the problem NOT occur? Always occurs

Did the problem NOT occur in any earlier versions? If so, what was the last version that worked? Nah

Workarounds: Honestly, none that I know off.

I've had this problem myself. It appears that the higher FPS rate you have, the more the animations flicker. Setting it to the default FPS rate looks a lot less choppy.
I think it's related to an old issue that was actually resolved:

"Movement states will now remain in use for a tick longer than before, instead of instantly reverting to a non-moving icon state the moment an atom steps on a tile, which made movement look kludgy if the atom kept moving."

The problem was that the movement state was flicking back to the non-moving states instead of cleanly looping them as long as the button is held. This is the exact same problem, as what's happening is your character is flicking to his non-moving state constantly. I fix this myself by making movement into a loop and manually changing the icon_state completely.
It's not exactly resolved. All the fix was was to extend the duration of movement, rather than completely fixing the problem. With higher FPS rates the ticks have a shorter duration, so that fix hardly helps.
I'm saying the issue was brought up earlier under different circumstances and was resolved. It's back now, and I'm saying it's more or less the exact same issue.
Oh, sorry. I guess I didn't completely understand that.
This problem is annoying :/ Hopefully it will be resolved soon.
In the next build the movement state will persist for at least 0.1s to avoid visual glitches.